1. Field of the Invention
This invention generally relates to integrated circuit (IC) fabrication and, more particularly, to a sputter deposition procedure for making a rare earth element-doped silicon-rich silicon oxide (SRSO) film with nanocrystalline (nc) Si particles, for use in electroluminescence (EL) applications.
2. Description of the Related Art
The observation of visible luminescence at room temperature, emanating from porous silicon (Si), has spurred a tremendous amount of research into using nano-sized Si to develop a Si-based light source. One widely used method of fabricating nanocluster Si (nc-Si) is to precipitate the nc-Si out of SiOx (x<2), producing a film using chemical vapor deposition (CVD), radio frequency (RF)-sputtering, and Si implantation, which is often called silicon-rich silicon oxide (SRSO). Er implantation, deposition (CVD), radio frequency (RF)-sputtering, and Si implantation, which is often called silicon-rich silicon oxide (SRSO). Er implantation, creating Er-doped nanocrystal Si, is also used in Si based light sources. However, state-of-the-art implantation processes have not been able to distribute the dopant uniformly, which may be important for high-efficiency light emission. Ion implantation also increases costs. Interface engineering may also be important for the device performance, but it is very difficult to achieve using ion implantation. All these drawbacks limit future device applications.
Other work (Castagna et al., “High Efficiency Light Emission Devices in Silicon”) describes a silicon-based light source consisting of a MOS structure with nc-Si particles and Er implanted in a thin oxide layer. After annealing at 800° C. for 30 minutes under nitrogen flux, the device shows 10% external quantum efficiency at room temperature, which is comparable to that of light emitting diodes using III-V semiconductors. However, the stability of the device is poor. Another device structure consists of a 750 Å thick silicon-rich oxide (SRO) gate dielectric layer doped with rare earth ions (Er, Tb, Yb, Pr, Ce) via ion implantation. After similar annealing, the device shows much more stable properties but the efficiency drops off to 0.2%
Undoped silicon nano particles possess a wide wavelength distribution in its light emission spectrum, due to its particle size distribution. On the other hand, RE doped SRSO emits light in discrete wavelengths correspondent to the intra 4f transitions of the RE atoms. For example, the main emission wavelengths for terbium, ytterbium, and erbium-doped SRSO are located at the wavelengths of 550 nm, 983 nm, and 1540 nm respectively. The monochromaticity of the RE-related light emission from doped silicon nano particles provides much better control over the wavelength, giving it wider application in optical communications.
To fabricate doped silicon-rich oxide, RE ion implantation has previously been explored. Although ion implantation provides for purity and flexibility, it is expensive and the dosage that can be implanted is limited. Dopant concentration in any particular depth direction is difficult to control and the concentration of dopant is not uniform.